Antibiotics are used for three major purposes in domestic animals: therapy, prophylaxis, and performance enhancement. The antibacterial feed additives, through their antimicrobial effects, will alleviate immune system challenges from the intestinal tract on the immune system. It is recommended that antibiotics for nutritional use should be restricted to those which are of economic value to livestock production, have little or no implication as therapeutic agents in man or animals, and which do not impair the efficacy of therapeutic antibiotics through the development of resistant organisms. In the EU, the legal use of chemotherapeutic feed additives requires an approval by a Community procedure as layed down in the Council Directive 70/524/EEC and its amendment (Directive 96/51/EEC, 5th amendment).